Materials with electric, magnetic, and elastic properties have been used for various applications for a long time. The electric properties of dielectric materials have been used in capacitors. The magnetic properties of permeable materials have been used in inductors. The elastic properties of certain materials have been used in springs. When in use these materials store and release energy at different times during their operating cycle via their internal forces of constraint that are require to maintain the material's physical properties.
Subclasses of these materials are materials in which there is a cross coupling of forces. Such cross coupling is exhibited in: piezoelectric1 materials where mechanical strain is a function of electric fields, and electric polarization is a function of mechanical stress; in magnetostrictive materials where mechanical strain is a function of magnetic fields, and magnetization is a function of mechanical stress; and in magnetoelectric materials where electric polarization is a function of magnetic fields, and magnetization is a function of electric fields. 1 The term “piezoelectric material” is meant to include any material whose mechanical properties depend on an electric field. This may include materials also known as electrostrictive materials.
These materials that exhibit cross coupling have been used in various transducer applications such as actuators and sensors. In general energy can be transformed from one form to another through this cross coupling. For example, in an actuator application electrical energy can be transformed into mechanical energy by means of piezo-electric or magnetostrictive materials.
However, none of the prior uses of these “cross coupled” materials has taken advantage of certain material properties through which a net loss of the material's internal energy over a complete cycle of operation is achieved without the need to raise the temperature of the material above ambient temperature.